The following disclosure relates to network devices and network communication.
Network management generally takes place between two types of systems, systems in control—called network management systems (NMS), and observed/controlled devices—called managed devices. Managed devices can include, e.g., hosts, servers, routers, repeaters, switches, and computers.
A management protocol is generally used to convey management information between a network management system and a managed device. One example management protocol is the Simple Network Management Protocol (SNMP). SNMP provides a way for network management systems to organize a large amount of information needed to manage a variety of managed devices.
A managed device typically includes specialized software modules, called agents, that access information about the managed device, and make the information available to a network management system. Managed devices maintain values for a number of variables and report the variables, as required, to a network management system. For example, an agent might report the number of bytes and packets in and out of a particular managed device, or the number of broadcast messages sent and received. In the SNMP Network Management Framework, each of these variables is referred to as a managed object. In the context of SMNP, a managed object represents anything that can be managed, or anything that an agent can access and report back to a network management system. A managed object can have a name, one or more attributes, and include a set of operations that can be performed by the managed object. Managed objects are typically contained in a Management Information Base (MIB), a database of the managed objects.
A network management system can control a managed device by sending an SNMP command to an agent of the managed device requiring the managed device to, for example, change the value of one or more variables. Commonly used SNMP commands include, e.g., GET-Request (retrieves one or more values from a managed object), SET-Request (updates selected variables of a managed object), and GET-Response (a reply to a GET-Request or a SET-Request). SNMP commands—including requests and responses—are sent between network management systems and managed devices as SNMP messages. An SNMP message is an SNMP protocol data unit (PDU) that includes message header elements defined by a particular Request for Comments (RFC).
When an SNMP command fails, a network management system typically sends an SNMP error code back to a user—e.g., a human network administrator. However, SNMP provides only a limited number of error codes. For version 1 of SNMP (SNMPv1), the following five error codes are supported: tooBig(1), noSuchName(2), badValue(3), readOnly(4), and genErr(5). See RFC 1157, Case, May 1990, A Simple Network Management Protocol (SNMP), incorporated herein by reference. For version 2 of SNMP (SNMPv2), the following 18 error codes are supported: tooBig(1), noSuchName(2), badValue(3), readOnly(4), and genErr(5), noAccess(6), wrongType(7), wrongLength(8), wrongEncoding(9), wrongValue(10), noCreation(11), inconsistentValue(12), resourceUnavailable(13), commitFailed(14), undoFailed(15), authorizationError(16), notWritable(17), and inconsistentName(18). See RFC 1905, Case, January 1996, Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2), incorporated herein by reference.
In some cases, more specific information about an error is known when an SNMP command fails. However, when a conventional SNMP protocol is used, the specific information about the error is not passed back to a user. Instead, the specific information about the error is converted (or mapped) into an error code that can generally only notify a user that a particular type of error has occurred. The error code typically does not convey why the error occurred. For example, an error code of wrongValue in response to a failed SNMP SET-Request command does not convey why the value associated with the SNMP SET-Request is wrong.